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[209.85.167.53]) by smtp.gmail.com with ESMTPSA id u1sm3894580lfu.24.2020.09.14.15.59.47 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Sep 2020 15:59:48 -0700 (PDT) Received: by mail-lf1-f53.google.com with SMTP id z19so1051345lfr.4 for ; Mon, 14 Sep 2020 15:59:47 -0700 (PDT) X-Received: by 2002:ac2:4ec7:: with SMTP id p7mr4498792lfr.352.1600124387573; Mon, 14 Sep 2020 15:59:47 -0700 (PDT) MIME-Version: 1.0 References: <20200821234958.7896-1-peterx@redhat.com> <20200821234958.7896-2-peterx@redhat.com> <20200914143829.GA1424636@nvidia.com> <20200914183436.GD30881@xz-x1> <20200914211515.GA5901@xz-x1> <20200914225542.GO904879@nvidia.com> In-Reply-To: <20200914225542.GO904879@nvidia.com> From: Linus Torvalds Date: Mon, 14 Sep 2020 15:59:31 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/4] mm: Trial do_wp_page() simplification To: Jason Gunthorpe Cc: Peter Xu , Leon Romanovsky , Linux-MM , Linux Kernel Mailing List , "Maya B . Gokhale" , Yang Shi , Marty Mcfadden , Kirill Shutemov , Oleg Nesterov , Jann Horn , Jan Kara , Kirill Tkhai , Andrea Arcangeli , Christoph Hellwig , Andrew Morton Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: A32F81803F9B0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 14, 2020 at 3:55 PM Jason Gunthorpe wrote: > > Just as an aside, the RDMA stuff is also supposed to set MADV_DONTFORK > on these regions, so I'm a bit puzzled what is happening here. Did the fork perhaps happen _before_ , so the pages are shared when you do the pin? MADV_DONTFORK doesn't mean COW doesn't happen. It just means that the next fork() won't be copying that memory area. That said, it's possible that the test cases do something invalid - or maybe we've broken MADV_DONTFORK - and it all just happened to work before. So it's possible the breakage is exposing some other bug.. Linus